Steering apparatuses such as illustrated in FIG. 12 are widely used for applying a steering angle to steered wheels (normally the front wheels) of an automobile. In this steering apparatus, a steering shaft 3 is supported on the inner-diameter side of a cylindrical steering column 2, which is supported by the vehicle body 1, so as to be able to rotate. A steering wheel 4 is fastened to the rear-end portion of the steering shaft 3 that protrudes further toward the rear than the opening on the rear end of the steering column 2. The rotation of the steering wheel 4 is transmitted to an input shaft 8 of a steering gear unit 7 by way of the steering shaft 3, a universal joint 5a, an intermediate shaft 6 and a universal joint 5b. The rotation of the input shaft 8 pushes or pulls a pair of tie rods 9 located on both sides of the steering gear unit 7, which applies a steering angle to the steered wheels according to the amount that the steering wheel 4 is operated.
The steering apparatus illustrated in FIG. 12 is provided with a telescopic mechanism for adjusting the forward-backward position of the steering wheel 4 according to the size and driving posture of the driver. The telescopic mechanism is constructed so that by fitting the front-end section of an outer column 10 on the rear side around the rear-end section of an inner column 29 on the front side so that relative displacement in the axial direction is possible, the steering column 2 has a telescopes shape, the overall length of which is able to extend or contract; and by combining an outer tube 11a and an inner shaft 11b by a spline joint, that steering shaft 3 is able to transmit torque, and can extend and contract.
Moreover, the steering column 2 and steering shaft 3 are constructed to be able to allow to displace the steering wheel 4 in the forward direction while absorbing impact energy during a collision accident. In other words, in a collision accident, after a primary collision in which an automobile collides with another automobile or the like, a secondary collision occurs when the body of the driver collides with the steering wheel 4, and in order to protect the driver by lessening the impact that is applied to the body of the driver during this secondary collision, the steering shaft 3 that supports the steering wheel 4 is supported by the vehicle body 1 so as to be able to move in the forward direction due to an impact load in the forward direction that occurs during the secondary collision. More specifically, the outer column 10 moves in the forward direction as the overall length of the steering column 2 contracts, and the outer tube 11a moves in the forward direction as the overall length of the steering shaft 3 contracts.
In recent years, as a measure to prevent automobile theft, automobiles have been equipped with various kinds of anti-theft apparatuses. One of these kinds of anti-theft apparatuses widely used is a steering-lock apparatus that does not allow operation of the steering wheel unless a proper key is used. FIG. 13 illustrates one example of a steering-lock apparatus as disclosed in JP 2008-265646 (A). This steering-lock apparatus 12 is provided with a lock unit 13 attached to part of the steering column 2a and a key-lock collar 15 having an engaging concave sections 14 formed in at least one location in the circumferential direction in a position that coincides with the phase in the axial direction of the lock unit 13, the key-lock collar 15 being fitted and fastened around part of the steering shaft 3. When operated (when locked), the tip-end section of a lock pin 16 of the lock unit 13 is displaced through a lock through hole 17 that is formed in the middle section in the axial direction of the steering column 2a toward the inner-diameter side of the steering column 2a, and by engaging with the engaging concave section 14, makes it essentially impossible to rotate the steering shaft 3a. In other words, when the steering wheel 4 is rotated with a force exceeding a specified value (value specified by the key-lock regulation) in a state in which the ignition key is turned OFF and the engaging concave section 14 and lock pin 16 are engaged, the steering shaft 3a will rotate with respect to the key-lock collar 15. However, when a force that is normally used for operating the steering wheel 4 is applied, the steering shaft 3 will not rotate. Steering-lock apparatuses having construction in which the key-lock collar 15 is fastened so as not to rotate relative to the steering shaft 3a, or having construction in which the key-lock collar 15 is integrally formed with the steering shaft 3a are also known. Furthermore, there are also steering-lock apparatus having construction in which breakage of the key-lock collar 15 or steering shaft 3a is prevented even when the steering wheel 4 is rotated with a force exceeding a specified value.
When the steering-lock apparatus 12 is assembled in the steering apparatus, the lock unit 13 is attached on the outer-diameter side of the steering column 2a, and the key-lock collar 15 is attached on the inner-diameter side of the steering column 2. Therefore, in order to arrange the key-lock collar 15 on the inner-diameter side of the steering column 2a so as to be able to rotate and to certainly allow the lock pin 16 and key-lock collar 15 to disengage without excessively increasing the stroke of the lock pin 16, it is necessary to make the outer diameter of the steering column 2a small and the inner diameter thereof large in at least in a portion of the steering column 2a where the steering-lock apparatus 12 is assembled, or in other words, it is necessary to make the thickness of the steering column 2a in that portion thin.
FIG. 14 illustrates an outer column 10a that is disclosed in JP 2007-223383 (A). The outer column 10a is integrally formed by die casting of a light alloy metal such as an aluminum alloy or magnesium alloy. Moreover, a fitting-holding portion 30 is provided in the end section in the axial direction of the outer column 10a for fitting the end section of a cylindrical shaped inner column inside so that relative displacement in the axial direction is possible, and a lock through hole 17a is provided in the middle section in the axial direction of the outer column 10a for assembling a steering-lock apparatus 12. With an outer column 10a having this kind of construction, there is a possibility that in the operated state of the steering-lock apparatus 12, the necessary strength will not be sufficiently maintained. In other words, when an attempt is made to rotate the steering wheel 4 with a large force in a state in which the lock pin 16 that protrudes through the lock through hole 17a into the inner-diameter side of the outer column 10a is engaged in the engaging concave section 14 of the key-lock collar 15, there is a possibility that the lock through hole 17a will deform due to an excessively large force. Therefore, in order to prevent such deformation, it is necessary to sufficiently maintain the strength of the outer column 10a. In order for this, the thickness of the outer column 10a can be increased, or the outer column 10a can be manufactured using an iron-based material, however, in that case a problem occurs in that the overall weight of the steering column increases.